1. Field of the Invention
The present invention relates to an apparatus and method for measuring the voltage of a plurality of cells contained in a battery pack.
2. Description of the Related Art
Generally, a high capacity battery pack used in electric vehicles, hybrid vehicles or the like, includes a plurality of cells capable of repeatedly charging and discharging. During charging/discharging of the battery pack, it is required to properly maintain the state of charge (SOC) of each cell and to protect the battery pack from abnormal circumstances such as over-charging or over-discharging. Thus, it needs to periodically measure and monitor the voltage of each cell using a cell voltage measuring apparatus.
FIG. 1 is a circuit diagram of a conventional battery cell voltage measuring apparatus 10.
Referring to FIG. 1, the conventional battery cell voltage measuring apparatus 10 comprises a floating capacitor (C), a first switch (SW1), a second switch (SW2), a cell voltage measuring circuit 20, an A/D converter 30 and a controller 40.
The first switch (SW1) is turned on by the controller 40 so as to make a cell voltage measurement. Accordingly, the voltage of each cell (B) is charged on each corresponding floating capacitor (C). After charging of the cell voltage, the first switch (SW1) is all turned off. When the first switch (SW1) is all turned off, the floating capacitor (C) is electrically isolated from the cell (B). Thereby the cell voltage is held on the floating capacitor (C).
After charging and holding of the cell voltage, the second switch (SW2) is subsequently turned on in order. Accordingly, the voltage (cell voltage) across each floating capacitor (C) is subsequently applied to the cell voltage measuring circuit 20.
The cell voltage measuring circuit 20 measures the voltage across each floating capacitor (C) subsequently applied thereto, and outputs an analog voltage signal corresponding to the voltage of each cell (B) to the A/D converter 30. Then, the A/D converter 30 converts the analog voltage signal into a digital voltage signal of a predetermined bit and outputs the digital voltage signal to the controller 40.
The controller 40 controls the overall operation of the first switch (SW1) and the second switch (SW2), and receives a digital voltage signal of each cell (B) outputted from the A/D converter 30 and stores the digital voltage signal in a memory (not shown). And, the controller 40 controls the charge/discharge of each cell (B) based on the digital voltage signal of each cell (B) stored in the memory, and performs various battery protection operations such as prevention of over-charging or over-discharging.
The cell voltage measuring circuit 20 includes a differential amplifier for outputting a voltage signal corresponding to the voltage across the floating capacitor (C) to the A/D converter 30. However, the conventional cell voltage measuring circuit 20 has cell voltage sensing lines L1 to L4 designed to measure the voltage of a plurality of cells using a single differential amplifier.
As shown in FIG. 1, the conventional cell voltage measuring apparatus 10 has cell voltage sensing lines L1 to L4 designed to measure the voltage of four cells using a single differential amplifier. Thus, when measuring the voltage of even-numbered cells, the polarity of the voltage across the floating capacitor (C) corresponding to even-numbered cells should be inverted. For this purpose, the cell voltage measuring circuit 20 has a polarity inversion circuit therein, which results in a complicated circuit structure of the cell voltage measuring apparatus 10.